If you're in the market for a new cellphone, you never have to step foot in a wireless store. Several retailers now can sign you up, however the process didn't work out so well for one woman.

This shows what can happen if two companies are involved in one transaction. Important paperwork slipped through the cracks. Leaving a Benicia woman stuck with a bill she did not deserve.

Benicia resident Linda Farmer is happy with her new iPhone, but not so happy with the headache that came with it.

It all began when she went to Best Buy and signed up for a new iPhone and contract with Verizon Wireless. The very next day, Sprint offered a better deal.

"Unlimited everything for my phone for the same price. So I said, 'Sure, why not?'" Farmer said.

She returned the Verizon phone to Best Buy, canceled that contract, and signed up with Sprint. It all seemed to go smoothly until she got a bill from Verizon saying she owed $553.

She was stunned when Verizon charged her for the phone she had returned. Farmer went back to Best Buy.

"They said, 'Do you have proof that you returned the phone?' I said, 'Yes, I have the receipt,'" Farmer said.

Best Buy promised to clear her bill. Instead, she got another Verizon bill demanding $553. Farmer called Best Buy, called Verizon, emailed copies of her receipt, but a month later Verizon sent her another bill.

"And then I was getting the threatening notices saying, 'You're way past due, you owe Verizon this $553,'" Farmer said.

The notice warned the debt could go to collections and damage her credit. She contacted 7 On Your Side, we contacted Best Buy, and it finally corrected her account with Verizon. The debt was finally gone.

Best Buy said: "We're happy we were able to resolve the situation. We never want to inconvenience our customers."

Verizon said: "We strive to provide the best possible experience for our customers at every touch point including through our national retail partners. We sincerely regret this error."

The case points out how important it is to keep receipts and any other documentation you have when you return any merchandise to a store. You never know when you'll need that proof.

Have you contacted the company but your complaint still isn't resolved? Have you asked to speak with a supervisor? Have you read the 7 On Your Side FAQs? If you live in the San Francisco Bay Area and you're still having trouble, 7 On Your Side wants to help you.